Potential Re-Gear idea

[JMH1980]

I have a 2016 XL Denali.
6.2L w/ 8L90E drivetrain.
It comes with the 3.23 ratio gearing.
Would replacing those with factory 3.42 gears have any huge positive impacts on drivability?

 

[Marky Dissod]

... 2016 XL Denali ... 6.2L, 8L90E ... 3.23.
Would replacing those with 3.42 have any huge positive impacts on drivability?

Short answer: NO.
Long answer: you used the word 'huge' - only going from 3.23 to 3.42 will not have a HUGE impact.
That said, of course it will have an impact. Provided you drive it 'less-than-enthusiastically',
more axle gear will improve city / metro / urban MpGs,
improve unladen highway MpGs (under 65MpH or so - over that speed, MpG benefits fade),
improve towing/hauling MpG
MpG benefits will NOT be HUGE, but they'll be measurable (unless you're leadfooted).

More assertive axle gear also takes some strain off the 8L90, so it'll go longer between rebuilds too.

Please note:
1. unless using VERY tall tires, 3.73 will be overkill with 8L90; 1st gear'll become almost useless
2. for maximum MpG & durability / longevity benefits, have your ecm and tcm tuned as well

 

[swathdiver]

^^^ Can't say it any better myself!

I knew a kid with an 8-speed in his leveled 5.7 RAM with 3.92 gears. That truck would walk away from my lifted 6.2 Sierra which has a 6-speed with 3.73s on 35s, effectively making it a 3.42 ratio. Comparing timeslips, it would be about equal to my other 6.2 Sierra with 3.42s, high 14s in the quarter mile.

Here are some examples of what your effective ratios and RPMs would be with the various gear ratios:

We just completed a gear swap about 1,500 miles ago, from 3.42s to 3.73s in my 2009 Yukon XL.

 

[swathdiver]

This is the chart that RAM uses with their ZF 8-speed and 3.92 gears.

So if you want gears and care little for the cost, consider steeper gears if you want more than an incremental improvement as I've done.

 

[B-train]

^^^ Can't say it any better myself!

I knew a kid with an 8-speed in his leveled 5.7 RAM with 3.92 gears. That truck would walk away from my lifted 6.2 Sierra which has a 6-speed with 3.73s on 35s, effectively making it a 3.42 ratio. Comparing timeslips, it would be about equal to my other 6.2 Sierra with 3.42s, high 14s in the quarter mile.

Here are some examples of what your effective ratios and RPMs would be with the various gear ratios:

View attachment 445688

View attachment 445689

View attachment 445690

We just completed a gear swap about 1,500 miles ago, from 3.42s to 3.73s in my 2009 Yukon XL.

How do you like 3.73s with the 6 speed? What driving dynamics changed - good or bad?

 

[swathdiver]

How do you like 3.73s with the 6 speed? What driving dynamics changed - good or bad?

1st gear is a little shorter than before. She moves out more briskly now and where there used to be a lag when you floored it from idle, that is no more. Part throttle acceleration is noticeably faster.

Fuel economy seems better in the city and about the same on the highway but I have not begun actually measuring that yet. She made 2 passes down the 1/4 mile so far and came out about 1 mph faster on average than before.

 

[JMH1980]

@Marky Dissod @swathdiver
Thanks for the information...

Doesn't seem reasonable to change anything up for minimal benefits like that.
I don't race or Off-road it. Might be some towing in the future. I guess the 3.42's would come in handy there. But I'll cross that bridge when it comes.

 

[swathdiver]

@Marky Dissod @swathdiver
Thanks for the information...

Doesn't seem reasonable to change anything up for minimal benefits like that.
I don't race or Off-road it. Might be some towing in the future. I guess the 3.42's would come in handy there. But I'll cross that bridge when it comes.

When you tow and are going up a steep grade, like Monteagle, just leave it in 4th or 5th gear. 5th would give you the equivalent of 4.10s.

Your best band for the buck is going to be a tune.

 

[JMH1980]

When you tow and are going up a steep grade, like Monteagle, just leave it in 4th or 5th gear. 5th would give you the equivalent of 4.10s.

Your best band for the buck is going to be a tune.

I am contemplating having a tune done for both engine and transmission. At 93,000 miles now and so far (knock on every piece of wood in sight) no transmission issues, other than changing fluid, filter and the lower harness, for the temperature sensor. The 8 speed seems to be decent for me.

 

[Marky Dissod]

When you tow and are going up a steep grade, like Monteagle, just leave it in 4th or 5th. 5th would give you the equivalent of 4.10s.
Your best band for the buck is going to be a tune.

It's an 8L90, bet that there are plenty of times when 6th would be enough.
Yes, it's tough to beat an ecm & tcm tune for bang for the buck.

Doesn't seem reasonable to change anything up for minimal benefits like that.
I don't race or Off-road it. Might be some towing in the future. I guess 3.42 would come in handy there. But I'll cross that bridge when it comes.

Only way to get more bang for the buck: combine 3.42 with the ecm & tcm tune.
That synergy would be HUGE - and it would not only eventually pay for itself,
it'd keep paying dividends in terms of longevity & durability. EDIT: and MpGs too.

(One of my suspicions is that engines would last even longer with better axle gearing.)

 

[fozzi58]

Not exactly relevant to OP's situation, but relevant to the conversation overall....

I went from 3.08's with the 6L80 to 4.10s. I did that mainly for racing.

On my daily tires which are 305/35 24s, RPMs are about 2250 at 75mph.
On my race tires which are 265/30 22s, The RPMs are closer to 2700 at 75mph.

I don't daily my race wheels but I have been on them for a few weeks at a time while trying to get my 24's powder coated, straightened, etc.

It was def too big of a jump and I think 3.55s or 3.73s would have been sufficient. I was running consistently above or below 14.1 at the track with the 3.08's. I should most definitely run a sub 14 with the 4.10's, the question is how sub am I going. I am hoping for a .5 second drop in ETs which would put me at mid 13's but that's high hopes.

I wish there was a way to change the final drive gear in the 6L80 cause a taller 6th would really just make the truck an overall pleasure to drive

 

[91RS]

What are you trying to accomplish? The difference won't be "huge," but it will be noticeable. You will likely get off the line a little faster, have a little less passing ability, and get slightly worse fuel economy. It'll probably tow better but I would feel it wouldn't be worth it for that unless you're towing every day. I don't feel it would be worth doing on a stock truck, but it might be if you have modifications in power, wheel/tire size, etc. it might be worth it depending on what exactly your goal is.

It is completely apples to oranges, but I did some gear ratio changes in my SS (which is a manual, weights a lot less than these trucks, and has a lot more power) but people were telling me that I wouldn't even notice going up or down one ratio, which was completely false. I went from the stock 3.70 to a 3.91, which was very aggressive off the line and cost me 2 MPG. Then I went to a 3.45, which was much better for daily driving but not aggressive enough for when I wanted that and now the car lugs a lot more. So, I'm going back to stock.

 

[swathdiver]

Not exactly relevant to OP's situation, but relevant to the conversation overall....

I went from 3.08's with the 6L80 to 4.10s. I did that mainly for racing.

On my daily tires which are 305/35 24s, RPMs are about 2250 at 75mph.
On my race tires which are 265/30 22s, The RPMs are closer to 2700 at 75mph.

I don't daily my race wheels but I have been on them for a few weeks at a time while trying to get my 24's powder coated, straightened, etc.

It was def too big of a jump and I think 3.55s or 3.73s would have been sufficient. I was running consistently above or below 14.1 at the track with the 3.08's. I should most definitely run a sub 14 with the 4.10's, the question is how sub am I going. I am hoping for a .5 second drop in ETs which would put me at mid 13's but that's high hopes.

I wish there was a way to change the final drive gear in the 6L80 cause a taller 6th would really just make the truck an overall pleasure to drive

Post up some timeslips next time out! I'll be taking mine back out as soon as the track opens up again.